Energy question of the week: Can the greenhouse gas carbon dioxide be stored safely underground?

Coal-fired power stations release more carbon dioxide per kWh than any other fossil fuel facility, and Germany has a large number of just this sort of power station. It is estimated that around 40 billion tons of coal are stored in potential open cast deposits in Lusatia and the Lower Rhine Basin. That makes up 14 percent of world reserves. The question is, can the carbon dioxide emissions be captured and stored underground?

The idea of filtering carbon dioxide out of coal power station exhaust gases and storing it underground is certainly very attractive. A pilot power station – Schwarze Pumpe in Lusatia – has been burning coal in pure oxygen since 2008; and it is possible to segregate the resulting carbon dioxide emitted by this oxyfuel process. Another power station in nearby Jänschwalde will soon be commissioned. Other approaches to filtering emissions are showing promise around the world, and segregating greenhouse gases should not be a major problem in the future. However, such processes consume energy, thus reducing the overall efficiency of the power station.

Test storage facility in Brandenburg

Segregation is only the first step; for real Carbon Capture and Storage (CCS), the carbon dioxide must be pumped down 1000 metres into porous rock, and stay there. Such a facility is being tested in Ketzin, Brandenburg, sponsored by the EU and the German Federal Government. Forty thousand tons of carbon dioxide have already been pumped underground. The project, called CO2SINK, is designed to test whether the gas will then remain underground reliably for decades or even centuries.

The safety of long-term underground storage of carbon dioxide is still an open question. Will such stores release their contents over time? Would this be hazardous for people and animals in the vicinity? This is a vanishingly small risk, but a loss rate of just one percent could sabotage all climate protection plans. This would mean that the majority of the stored gas would gradually be released into the atmosphere. To deal with this, experts have suggested that the escaping gas should be captured and pumped back down again. But this solution requires pumping over a very long time. This would not only be very expensive, but would require long-term management of the stores, which critics of the CCS concept are already comparing to the disadvantages of long-term nuclear waste storage.

Potential carbon dioxide stores in German have only limited capacity

In Germany, the main candidate for carbon dioxide storage is the North German Plain. But just how much carbon dioxide could actually be stored there is not yet clear. Optimistic estimates by supporters of CCS suggest that the area could handle at most 8 to 10 billion tons of gas. This – as yet uncertain – amount would assure at most 30 years of storage for power station emissions of 300 million tons a year. The population in potential storage areas is already starting to resist the idea, due to the unknown risks associated with it.

At the current state of CCS technology, it will still be 20 to 25 years before segregation and storage processes are ready for large-scale deployment. It is questionable whether this expensive technology, with its long-term (over centuries) management requirements, would make economic sense in Germany. But energy hungry countries with large coal deposits, such as China, may see CCS as an option for dealing with carbon dioxide emissions.

The DLR Energy question of the week in 'The future of energy' Year of Science

The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog.

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Energy journalist Jan Oliver Löfken writes among other things, for the Technologie Review, Wissenschaft aktuell, Tagesspiegel, Berliner Zeitung and P.M. Magazin on issues involving energy research and industry. For DLR, he answered the Energy question of the week during the Year of Energy 2010.
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